1. Field of the Invention
The present invention relates to a rotary evaporator.
2. Description of the Prior Art
Rotary evaporators are known which are used to evaporate substances, particularly to evaporate solvents when pharmaceutical or chemical products are concentrated or distilled. With these known rotary evaporators, the liquid substances to be evaporated are placed into the hollow chamber of a rotatable rotating flask (evaporation vessel), usually in a heating bath. By rotating the flask, a thin liquid film is formed on the inside of the rotating flask and the substances, especially the solvent, then evaporate from this film. Some of the substance or solvent also evaporates directly from the surface of the liquid that is in the rotating flask. The vapor is conveyed from the rotating flask via a vapor line to a condenser, where it condenses out again. Generally speaking, a negative pressure or a vacuum is also generated in the rotating flask in order to raise the vapor pressure of the substances to be evaporated and to protect the product. In a passage area, the vapor line is joined to the rotating flask via a rotatable connection. The connection site is sealed off by of a rotary gasket.
German patent specification DE 1 224 062 discloses a rotary evaporator with a rotating flask that can be rotated around its axis of symmetry. The rotating flask is placed tightly on the standard tapered-ground joint of a glass adapter whose tapered part is inserted into the conical bore of a support ring having a worm gear crown. For purposes of driving the rotating flask, a screw attached to the drive shaft of a small electric motor equipped with a switch then engages the worm gear crown. The support ring can rotate in a ball bearing of a housing to which the motor as well as a condenser are affixed. The work flask can also pivot freely around a swiveling axis that runs perpendicular to its axis of symmetry. For this purpose, the housing has a bearing plate into whose bore a rigid, horizontal guide shaft of the apparatus stand has been inserted so as to rotate freely, as a result of which the rotating flask can move freely around the guide shaft or the swiveling axis in a radius until it is floating freely on the surface of a water bath.
The free movement around the swiveling axis or pendulum axis parallel to the axis of symmetry of the rotating flask theoretically makes it possible to concentrate any quantity of liquid in a large rotating flask of any desired size, whereby the flask size or the quantity of liquid to be concentrated in one operation is only limited by the size of the rotating flask that still allows comfortable use without requiring a special lifting and lowering mechanism. Therefore, with a rotary evaporator having such a pendulum system, the weight of the rotating flask, together with the substance to be evaporated that is in the flask, is held up in the water bath exclusively by the buoyancy of the rotating flask, as a result of which torques and forces acting upon the rotating flask holder are markedly reduced. A thumb screw on the bearing plate serves to hold the rotating flask in any desired slanted position (swiveling position), also independently of the water bath.
Together with the rotating flask affixed to the glass adapter, the latterxe2x80x94which can be rotated by means of the rotary drivexe2x80x94is sealed by a gasket with respect to another, non-rotating glass adapter connected to the housing. This stationary glass adapter is connected to the other parts of the rotary evaporator apparatus by means of a bellows made of pure polytetrafluoroethylene. The bellows serves to compensate for the relative movement between the pivoting unit consisting of the rotating flask, the drive means, the housing and both glass adapters as well as the stationary apparatus stand that does not swivel along with the unit. This swiveling axis runs through the bellows in the vicinity of its point of intersection between both diagonals. The bellows can be deformed during the swiveling motion around an initial position in which its center axis runs essentially vertical, that is to say, parallel to the force of gravity. The swiveling axis for the pendulum movement of the rotating flask and the axis of symmetry of the rotating flask, which is provided as the axis of rotation, intersect at a point of intersection and thus lie on the same plane in every swiveling position. Therefore, the bellows is positioned laterally offset parallel to the swiveling axis, relative to the rotational movement of the stationary glass adapter of the rotating flask.
In order to remove precipitate that forms in the glass adapters, according to German patent specification DE 1 224 062, a delivery and washing nozzle is installed on the side of the stationary glass adapter that faces away from the glass adapter that rotates, said nozzle serving to spray a rinsing fluid, which is fed via a two-way tap, against the inside walls of the glass adapters. Any precipitate that might be present in the glass adapters can.be removed in this manner and returned to the rotating flask, together with the liquid that is being newly introduced.
German application DE 35 22 607 A1 discloses another rotary evaporator having a pendulum system. With this rotary evaporator, the weight contained in the rotating flask or changes in this weight as the rotating flask enters the bath liquid are ascertained by weighing, and the result of the weighing is employed as the regulating or control parameter for the evaporation process. With this known rotary evaporator, the pendulum axis or swiveling axis is likewise arranged perpendicular to the axis of rotation; however, the pendulum axis does not run in the same plane as the axis of rotation but rather, as seen in the direction of gravity, the pendulum axis is arranged below the axis of rotation of the rotating flask. In the working position of the rotating flask, the axis of rotation creates an acute angle with respect to the vertical, in other words, with respect to gravity, so that the rotating flask is immersed into the liquid bath downwards at an angle. On the one hand, a drive part that drives the flask neck with the rotating flask around the axis of rotation is mounted in a swiveling bearing so as to swivel on a stand around the pendulum axis, and on the other hand, the drive part is damped against the swiveling motion by a shock absorber that is likewise attached to the stand. On the side of the drive part that lies opposite from the rotating flask, there is a vapor pipe that does not rotate around the axis of rotation, but that swivels around the pendulum axis. The product to be introduced into the evaporation process is fed in parallel to the axis of rotation at the free end of the vapor pipe. A branch leads essentially horizontally from the vapor pipe to a condenser, where the evaporated product condenses and runs down as distillate into a distillate receiving vessel. In order to compensate for the pendulum movement of the vapor pipe relative to the drive means and of the rotating flask relative to the stationary condenser, a compensating element is installed in the branch. The center axis of the compensating element, which matches the direction of flow of the vapor, runs essentially horizontal.
If, like in German patent specification DE 1 224 062 or with the rotary evaporator according to German application DE 35 22 607 A1, a bellows is employed as the compensating element, under unfavorable conditions, precipitates can form in the bellows which, due to the horizontal arrangement of the bellows, can accumulate in the lower folds and can no longer drain. Moreover, the compensating element in German application DE 35 22 607 A1 is located relatively far away from the pendulum axis, as a result of which the compensating element undergoes a relatively strong deformation, especially bending, stretching and/or compression, during the pendulum movement, which can give rise to malfunctions in actual practice under certain conditions.
Accordingly, an object of the present invention is to provide a rotary evaporator with a pendulum system with which the above-mentioned drawbacks encountered in the state of the art are overcome, at least in part, or are at least reduced.
This and other objects of the present invention which will become apparent hereinafter, are achieved by providing a rotary evaporator including:
a) a rotating flask for holding a to-be-evaporated substance,
b) a drive means to rotate the rotating flask around an axis of rotation (turning axis) that runs through the rotating flask,
c) whereby the rotating flask additionally can be swiveled around a swiveling axis (pendulum axis) which
c1) runs outside of the rotating flask and,
c2) relative to the force of gravity, runs (is arranged) above the axis of rotation of the rotating flask.
A special advantage of the arrangement of the swiveling axis above the axis of rotation is that the area below the axis of rotation remains free and other components can be accommodated in this lower area. This allows a compact structure of the rotary evaporator. The terms axis of rotation and swiveling axis refer to geometrical axes or, expressed in mathematical terms, straight lines in space.
In a preferred embodiment, the axis of rotation is aligned essentially orthogonally to the swiveling axis. Preferably, the rotating flask is designed so as to be at least approximately rotationally symmetrical with respect to a center axis of the rotating flask in order to attain a uniform moment of inertia. Generally speaking, the axis of rotation coincides with the central axis of the flask, as a result of which unbalances are avoided during the rotational movement. The rotating flask is also generally mounted in at least one rotary bearing so as to be able to rotate around the axis of rotation.
In an advantageous embodiment of the inventive evaporator, for purposes of transporting the evaporated substance(s), the rotating flask is connected to one end of a vapor line that does not rotate along with the rotating flask. Another end of the vapor line is then preferably connected to a condenser for the condensation of the evaporated substance(s). The condenser is preferably arranged above the vapor line, relative to the force of gravity.
A particularly advantageous embodiment of the rotary evaporator is characterized in that there is at least one flexible compensating element in the vapor line. Here, a first vapor line segment extending between the rotating flask and the compensating element can be swiveled together with the rotating flask around the swiveling axis, while a second vapor line segment, which follows the compensating element and generally leads to the condenser, cannot be swiveled together with the rotating flask around the swiveling axis. The compensating element connects the two vapor line segments with each other so that they permit flow and it compensates for the position change between the two vapor line segments that is caused by the swiveling motion. The compensating element is usually a bellows or a flexible tube.
Preference is given to an embodiment in which the swiveling axis intersects the vapor line, that is to say, it runs through the vapor line. In this manner, leverage forces and moments of inertia can be kept low. It is particularly advantageous if the swiveling axis runs through the compensating element, preferably at least approximately through a mid-point of the compensating element, especially through a point of intersection of two diagonals of the compensating element. As a result of this, the deformation of the compensating element during the swiveling motion can be kept to a minimum.
Preferably, the second (stationary) vapor line segment is positioned essentially parallel to the force of gravity, at least in the area of the end that is connected to the compensating element.
In an advantageous embodiment, the rotary evaporator comprises a liquid bath into which the rotating flask is immersed or can be immersed, whereby the immersion and/or the position of the rotary evaporator in the liquid bath is established or changes automatically in response to the swiveling motion around the swiveling axis. The liquid bath generally serves as a source of heat for setting the process temperature in the rotating flask.
The rotating flask can preferably be freely swiveled around the swiveling axis within a prescribed swiveling range so that the swiveling angular position of the rotating flask and thus its position in the liquid bath are established on their own, due to the buoyancy of the rotating flaskxe2x80x94with the substances it containsxe2x80x94in the liquid bath. As a result, the bearing and the holding brackets of the rotating flask are relieved of torques and leverage forces. Naturally, aside from a free swiveling bearing, it is also possible to provide a swiveling drive means in order to achieve a specific setting of the swiveling position of the rotating flask.
As a rule, the rotating flask faces downwards at an angle, in other words, it can be swiveled within a swiveling range between a position of the axis of rotation that is horizontal, that is to say, perpendicular to the force of gravity, and a position of the axis of rotation that is oriented vertically downwards, in other words, parallel to the force of gravity.
The arrangement of the swiveling axis with respect to the axis of rotation is preferably such that a vertical reference plane encompassing the axis of rotation and the force of gravity lies essentially perpendicular to the swiveling axis and, in every swiveling position of the rotating flask, the point of intersection of this reference plane with the swiveling axis, relative to the force of gravity, lies above a point of intersection of the axis of rotation with a vertical straight line that runs through the point of intersection of the reference plane with the swiveling axis in the direction of the force of gravity.
In a particularly advantageous embodiment, the swiveling axis is near the axis of rotation in order to keep the deflection or deformation of the compensating element small and/or the vapor path as short as possible. The distance between the swiveling axis and the axis of rotation preferably lies within a range from two times to six times the value of a diameter (or: a clear width) of the cross section of the vapor line.
In another embodiment, in a first line segment, the vapor line has a transition area, especially a bend, between a first area that runs parallel or coaxially to the axis of rotation and a second area that runs essentially perpendicular towards the swiveling axis. As a result of the angle created between the two areas of the first vapor line segment or the bend, the vapor path can make a direct transition from a partial path parallel to the axis of rotation to a perpendicular partial path, that is to say, parallel to the force of gravity so that a practically minimal vapor path can be achieved in the ascending direction of the vapor.
A reflux unit of the rotary evaporator is formed in that the condenser has a distillate receiver that is or can be connected via at least one closure element to a distillate vessel and in that, when the closure element is closed and the distillate receiver has been filled, distillate flows back into the rotating flask via the vapor line. The condenser is preferably positioned perpendicularly so that the force of gravity causes distillate to flow into the distillate receiver that is preferably arranged in the lower area of the condenser. The pronounced steepness or even vertical position of the vapor line is particularly advantageous for the return of the distillate since the force of gravity makes the distillate flow rapidly and without residues back into the bellows, for example. The distillate can also be returned to the rotating flask via another line which is optionally connected to another closure element located downstream from the distillate receiver.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.